Ages 8–10: plant the seed
Keep it factual and short. "When your body is ready — usually somewhere between 10 and 14 — you'll start having periods. It's a bit of blood from your tummy, once a month, for a few days."
Normalise it in passing: buy pads on the shopping trip, mention when you're on yours, don't whisper the word.
Ages 10–12: the practical talk
Walk through what a pad is, how to put one in underwear, how often to change it (every 3–4 hours during the day), and where the bin is in school toilets.
Agree a signal — a code word by text or a specific emoji — so she can quietly tell you she's started or needs help.
Ages 12+: full picture, no lectures
By now she likely knows most of it from friends, school, or TikTok. Your job is to be the trusted correction: "Some of what you'll hear is right, some isn't. Ask me anything and I'll tell you the truth or find out."
Introduce that periods aren't just bleeding — mood, energy, sleep and appetite all shift across the month.